Complex dithiophosphoric acid esters



Patented Apr. 17, 1945 Elmer w. Cook. New York. N. Y. and William D.

Thomas, Jr., Stamford, Coma. assign orsto American Cyanamid Company, New York. N. a corporation of Maine No Drawing. Application June 5. 194:.

s n-.1 No. mszo Claims. (Cl. 280-481) This invention relates to complex esters of dithiophosphoric acid and to salts thereof. The invention includes the complex dithio'phosphoric acid esters themselves as hereinafter defined, the

salts thereof with monovalent andpolyvalent metals and other salt-forming bases, and the methods of preparation of said complex estersand their salts. i

It is known that simple esters of dithiophosphoric acid are formed by heating 4 molecular proportions of a primary, secondary or tertiary monohydric alcohol or a monohydric phenol with 1 molecular proportion of PzSs until the evolutionof hydrogen sulphide is substantially completed. It is also known that these simple esters will form salts with monoor polyvalent metals and other salt-forming bases by agitating the acid ester with a solution or suspension of an oxide, hydroxide or carbonate of the base. It is a principal object of our present invention to provide a class of complex dithiophosphoric acid esters similar in general characteristics to the simple esters that have just been described, but which contain a monocarboxylic acid chemically combined with the dithiophosphoric acid radical. Many of these complex esters and their calcium, barium, zinc and other heavy metal salts have been found to' be soluble in lubricating oils and to possess valuable properties as anti-oxidants, detergents and corrosion inhibitors when the lubricating oil is used in the crankcase of an internal combustion engine under heavy duty service conditions.

The complex dithiophosphoric acid esters of the invention are prepared by reacting a mixture of one or more monohydric alcohols or monohydric phenols and one or more monocarboxylic acids used.

cally combined along with the alcohol or phenol The complex esters prepared by the abovedescribed process are mixed monocarboxylic acid anhydride-alcohol condensation products of phosphorous pentasulflde. The compositions in which less than 2 mols oi monocarboxylic acid and more than 2 mols of monohydric alcohol or with P285 until the evolution of hydrogen sulfide is completed. With alcohols and acids of low molecular weight the reaction takes place withevolution of heat. With higher alcohols and phenols and with the higher and less reactive monocarboxylic acids a moderate .amount of heatin should be applied. Suitable reaction temperatures are about 9.0-l20 C. In general. at least 2 mols of monohydric alcohol or phenol and one mol of monocarboxylic acid should be used ior each mol of Pass and the remaining molecular equivalent may consist entirely of monocarboxylic acid or of monohydric alcohol or phenol or partly of monocarboxylic acid and partly of alcohol or phenol. when the hydrogen sulfide evolution is complete a heat-stable complex is formed in phenol are condensed with one mol of P285 are probably mixtures, but those in which equlmolecular quantities of acid and alcohol or phenol are reacted with P185 are compounds of definite chemical constitution and may be defined by the following structural formula:

4 r R0/ s-n wherein R is the residue of a monocarboxylic acid and R. is the residue of a monohydric alcohol or phenol. This formula, which represents a replacement of one of the alcohol groups of a diester of dithiophosphoric acid by a carboxylic acid, is consistent with the formation of heavy metal salts as well as with the behavior ofthese salts in crankcase oils.

The complex dithiophosphoric acid esters corresponding to the above iormula form salts by simple replacement of the hydrogen of the SH- group with sodium. potassium. ammonium and other salt-forming bases, With divalent metals such ascalcium. barium, strontium and zinc two molecules of the complex dithiophosphoric acid radical are combined with each atom of metal. while three such molecules are combined with trivalent metals such as aluminum. etc. Accordingly the compounds of the present invention, including both the free acid esters and their salts,

\ are defined by the formula:

wherein R and R are as defined above, M is hydrogen or a salt-forming base such as magnesium, nickel, tin. sodium. barium. aluminum, chromium. cobalt or any other-suitable metal. or ammonium. quinoline. morpholine and the like, and a: is the valence oi M. The metal salts are preferably prepared by agitating a reactive oxide, hydroxide or carbonate of the metal with a solution of the complex ester in a mixture of alcohol and toluol. The salts with ammonium and with organic bases which the monocarboxyllcacid radical is chemiare prepared simply by reacting th acid esters with the free base in the presence of a suitable solvent such as alcohol or an. alcohol-toluol mixture. From the foregoing it is evident that any suitable esterifying agents may be used in preparing complex dithiophosphoric acid esters for use in practicing the present invention. Lower aliphatic alcohols which may be used either singly or in admixture are methyl, ethyl, propyl and the various isomeric butyl and amyl alcohols, and particularly the cheap mixtures of amyl alcohols sold commercially as fusel oil and those obtained from low-boiling petroleum fractions and sold as Pentasol. Higher aliphatic alcohols such as hexyl, heptyl, octyl, nonyl, decyl, lauryl, myristyl, stearyl, oleyl and octadecyl alcohols and the like also may be used, either singly or in admixture.

Certain fractions containing substantial quantities of alcohol mixtures can alsobe used in preparing compounds representative of the present invention such as, for example, the mixtures of branched-chain alcohols obtained as by-prodnets in the commercial hydrogenation of oxides of carbon in the presence of promoted copper chromite catalysts. Among the most important sources of alcohol mixtures of this type are the so-called "H. T. P. alcohols. One of the most important fractions from this source is the socalled "B-24 alcohol fraction, which has the following composition:

B. P. about 178 c 4-methyl heptanol-l, B. P.

about 185 C Secondary alcoholsunidentifled ....do -34 histories-unidentified ..-do 18 Esters ..do 3

Tentative identification present.

Another class of mixed higher branched-chain probably other alcohols also alcohols that we have found suitable for use in the preparation of complex dithiophosphate heavy metal salt additives for crankcase lubricants are those obtained by the reduction of the corresponding higher aliphatic ketones with hydrogen. Thus, rearrangement of alpha, betaunsaturated ketones produced by the condensation of ketones of lower molecular weight may be employed. Typical alcohols that can be produced cheaply by the method are i-methyl hexanol-2, 5-methy1 hexanol-3, .--rnethyl heptanol-2 and fi-methyl heptanol-B.

In addition to the aliphatic alcohols and alcohol mixtures, the aromatic alcohols such as benzyl alcohol and particularly the phenols form another important class of ester-forming compounds for use in preparing the compositions of the present invention. Phenols, such as phenol itself, cresol, xylol and xylenol may be used as well as higher alkyl phenols having larger oilsolubilizing aliphatic groups. Typical phenols of this class are p-tertiary amyl phenol, tertiary butyl phenols and particularly the'di-alkyl phenols such as 2,4-dipropyl, dibutyl or diamyl phenols. Complex esters of dithiophosphoric acid .with phenols of these classes are both oil-soluble and heat-stable, and when used in the form of their heavy metal salts they possess excellent detergent. properties for crankcase oils.

Any saturated organic monocarboxylic acid may be used in admixture with a monohydric alcohol or phenol in preparing the complex dithiophosphoric acid esters of the invention. When improved oil-solubility is desired we prefer to employ cyclic or acyclic monocarboxylic acids which contain oil-solubilizing groups, such as the higher aliphatic monocarboxylic acids, by which term we include all those carboxylic acids of the aliphatic series which contain at least 6 carbon atoms. Representative acids of this class which may be employed are caproic and other isomeric fatty acids of 6 carbon atoms, caprylic, pelargonic, lauric, myristic, palmitic and stearic acids. Saturated fatty acid mixtures obtained from ani- -mal and vegetable oils and fats, such as coconut oil and palm oil, may also be used.

Representative saturated and unsaturated cyclic carboxylic acids that may be employed include the naphthenic acids, which are cycloaliphatic monocarboxylic acids of about 8 or 9 to 20 carbon atoms, abietic acid, dihydroabietic acid, benzoic acid, alkyl-substituted benzoic acids and the like.

Where oil-solubility is not of particular importance, lower aliphatic monocarboxylic acids may be employed in admixture with alcohols of relatively low molecular weight, thereby producing esters which contain a higher percentage of phosphorus and sulfur. Representative lower fatty acids that may be employed include acetic acid, proprionic acid, butyric acid and the like, and these may be used in conjunction with lower aliphatic alcohols such as ethyl, propyl, isopropyl 40. and butyl alcohols or in admixture with alcohols of higher molecularweight if desired.

The invention will be illustrated in detail by the following specific examples. It should be understood, however, that although these examples may describe in detail certain of the more specific features of the invention they are given primarily for purposes of illustration, and the invention in its broader aspects is not limited thereto.

Example 1 addition of a water solution containing 4 grams of NaOH followed by evaporation to dryness. The product was a yellow solid that was easily soluble in water.

Example 2 50 parts by weight. of amyl alcohol, 50 parts of 13-24" alcohol, 21 parts of lauryl alcohol and 40 parts of lauric acid were mixed together and 72 parts of P285 were added. The mixture was heated with agitation at -l05 C. for about-2.5 hours, or until the evolution of H28 was substantialy complete. The product was decanted from as'rasu 3 the small remaining amount of Past and was the complex dithiophosphoric acid ester was obtained as a reddish-yellow liquid. neutralized-by adding 83.25 parts by weight of 215 parts by weight of the complex dithiophos- 92% barium oxide for each 340 parts of the acid phoric acid ester obtained by this procedure was ester as described above. The product was disdissolved in a mixture of 56.5 parts of ethyl al- 5 solved in l-W grade lubricating oil to form a cohol and 125 parts of Solvesso No. 1" (an clear 50% solution. aromatic petroleum solvent consisting mainly of Example 5 toluol) and 44.5 parts of finely ground barium 81 h 1 50 m oxide was added to this solution while stirring B by Weight amyl Pa vigorously and maintaining'the temperature at 0 of 91601101, 21 p ii of lauryl alcohol and about 3035 C. After filtering the resulting solu- 40 parts 9 hydrogenated i wgre mlxed with tion from insoluble matter the alcohol was reof P255 and the mlxture was heated at moved by vacuum distillation'the residue was 110-115 C. for about two hours. After dissolvsolved in grade motor on and the remain ing the product in ethanol and toluene, filtering, ing volatile solvent was removed by a second figg s ggz fizfi g fig gg i gi gg gg vacuum distillation. The product was obtained weight of zinc om de for each 189 parts of the as a clear 50% solution of the barium salt of the complex ester. The insolubles were filtered oflE complex dithiophosphoric acid ester in lubricatmg on and the solution evaporated under a vacuum Example 3 and dissolved in lubricating oil to a 40% soluparts'by weight f fuse} 011, 23 parts of-lauryl tion. In the same manner the barium salt w alcohol, 105 parts of palm'ltic acid and 56 parts also Preparedof P285 were reacted by heating together with Example 7 vigorous agitation at 95-105 C. for about 2 hours, Complex te w r prepared containing or until the evolution of H25 was complete. 25 chlorosteario acid, p-hydroxy phenyl stearic 518 parts by weight of the complex acid ester I acid, naphthenic acid and other fatty acids in the was dissolved in a mixture of equal parts of manner described in the preceding examples and ethanol and toluol, filtered, and 83.25 parts by converted to their heavy metal salts in the usual weight of 92% barium oxide was added. After manner. The reagents employed and the comagitation to complete the salt formation at bining weights of the complex dithiophosphoric 30-35 C. the insolubles were filtered off and the acid esters formed are shown in the following solution was evaporated under a vacuum and distable wherein the quantities given are in parts solved in a lubricating oil-of l0-W grade. The by weight: 1

N aphthanic Myristic Paimiflt' 9,i0 dichlorostearic p-Hydroxy-phenyl-stearia. a 60 i s- Molecular equivalent 752 705 378 647 last traces of the toluolwere then stripped off 'by The complex dithiophosphoric acid esters -prevacuum evaporation. A% solution of the prodpared as described in this table were converted not in lubricating oil was clear at ordinary atmosinto their Ba, Ca, Sr and Zn salts, in each case pherio temperatures. by dissolving the free acid ester in a mixture of Example 4 equal parts ofeethanol and toluene and adding one-half the molecular equivalent of barium 50 P r y weight of amyl 8.1 01 1. 50 9 of oxide, calcium oxide, strontium oxide or zinc Is-24" alcohol and 50 parts of myris c d Were oxide, based on the molecular weight of the ester reac ed Wi h '7 Parts Of P2 5 by heating as in as shown by its-neutralization number. The re- Exam 2. e p d c was decanted. dissolved sulting salts were dissolved in lubricating oils and in an aleehel-toluene m and the barium the solutions freed from volatile solvents by heatsalt formed by neutralization with 92% barium m under u oxide on the basis of 448 parts of the complex di- Example 8 thiophosphoric acid ester for each 83.25 parts of added barium oxide. The solvent was driven off R entative samples of th Products pr and the salt dissolved in lubricating oil of 10-W pared as described i the Preceding a p were tested for efiiciencyby the Underwood and 30 grade to form clear 50% solutions as in the Oxidation test. This test consists in heating preceding examples.

. 1500 cc. of the oil under test to 325 F. and con- Emmple 5 tinuously spraying a portion of the heated oil A mixture of 50. parts by weight of amyl alcoagainst a. 2" 'x 10" freshly sanded copper strip he], 50 parts B-24 alcohol and 50 parts of lauric and two freshly sanded hearings to be tested acidwere reacted with 76 parts of P285 as in the for corrosion for five hours while permitting precedingexampla. The equivalent combining free circulation of air through the apparatus. weight of the product was determined by its neu- Samples of the oxidized oil were then examined tralization number as being 340 and therefore i for specific gravity, neutralization number, and

naphtha insoluble and the bearings under test were weighed to determine loss by corrosion. The results were as follows:

The oil used in all the above tests was a Mid- Continent-base solvent-refined S. A. E. iii-grade motor oil to which 0.01% FezOs was added in the form of iron naphthenate. A slightly difierent oil of the same base was used in testing the prodnot of Example 6-No. 3. In all cases 0.5% or the barium salt of the complex dithiophosphoric acid ester was used in the oil tested.

Iron naphthenate' is known to be a powerful promoter of oxidation and decomposition in lubricating oils. Compounds similar to this substance are usually present in engines containing oxidized oil as a result of the attack on the metal by the acidic oxidation products. The efiectiveness of the heavy metal salts of complex dithiophosphoric acid esters in overcoming the decomposition caused by iron salts of naphthenic acids is another important advantage of the present invention.

' Example 9 Another widely used test for accelerated oxidation in crankcase oils is known as the Catly'tic Indiana test. The apparatus consists of a constant temperature bath maintained at 341 F. in which a number of large glass test tubes are immersed. 300, cc. samples of the oil under test are poured into these tubes and air at the rate of 10 liters per hour is bubbled through the oil. In order to reproduce the conditions existing in the crankcase of an engine weighed strips of copper-lead alloy are suspended in the oil samples. As metallic surfaces, particularly copper, greatly accelerate the rate of oxidation and decomposition of the oil in the presence of oxygen this is an important factor in the test. Bearing corrosion rates can also be determined by again weighing the strips after 70 hours immersion, which is the usual test period.

The barium salts of representative samples of the complex dithiophosphoric acid esters prepared as described in preceding examples were also evaluated by this test. A Mid-Continent solvent-refined S. A. E. IO-grade oil was used. In all cases except the control the oil contained 1% by weight of the additive. The results are shown in the following table.

After completion of the tests the oil was removed and the amount and character of any sludge adhering to the walls of the tubes was noted. In all cases where additive was present in the oil there was only a slight amount of sludge, and these deposits were soft and easily removed by brushing.

This is a continuation-in-part of our copending application Serial No. 452,888 filed July 1942.

What we claim is:

1. A dithlophosphoric acid ester or the formula:

ac 0.0 s 1 iM 1220 s-Jz in which R is a saturated hydrocarbon radical,

R is the residue of a member of the group con-- sisting of monohydric alcohols and phenols, M

is a member of the group consisting of hydrogen and salt-forming bases, and :c is the valence of M.

2. A dithiophosphoric acid ester of the formula:

R.C0.0\ %s 1 P M Alk.O \S r in which R is a. saturated hydrocarbon radical, Alk is an alkyl radical. M is a. member of the group consisting of hydrogen and salt-forming bases, and a: is the valence of M.

3. A dithiophosphoric acid ester of the formula:

A1k.co.o s

P M 1120 s- 1: I

Alk.O 0.0 /S

y M I Alk.0 S- I in which each Alk is an alkyl radical, M is a member of the g'roup consisting of hydrogen and salt-forming bases and a: is the valence of M.

5. A method of producing a complex dithiophosphoric acid ester of the formula in which R is a saturated hydrocarbon radical and R. is the residue of a member of the group consisting of monohydric alcohols and phenols which comprises reacting with P285 an equimolecular mixture of a saturated unsubstituted monocarboxylic acid and a member of the group .consisting of monohydric alcohols and phenols until evolution of hydrogen sulfide is completed.

ELMIER W. COOK.

D. THOMAS, JR. 

